1. Field of the Invention
The present invention relates to a body to be plated having a structure to determine whether or not the film thickness of plating formed on the body to be plated is within a specification, a method of determining a plated film thickness, and a method of manufacturing a semiconductor device.
2. Description of Related Art
Plated film thicknesses are occasionally measured in inspection processes for bodies to be plated to which plating is applied. In semiconductor devices, for example, exterior plating (e.g., solder plating) is applied in order to facilitate mounting lead terminals on substrates. In exterior plating, it is necessary to obtain proper film thicknesses (hereinafter called “plating thicknesses”) and proper composition (e.g., Sn and Bi) in order to ensure the mounting quality. Therefore, electrical currents flowing to electrodes and plating liquids in which semiconductor devices are submerged and the likes are carefully controlled in plating operations. However, when plating operations continue, process conditions of the currents and the plating liquids begin to fluctuate, and consequently causing a problem that the plating thicknesses and the composition become unsuitable.
FIG. 10 shows a typical flow for a manufacturing process of semiconductor devices in the related art. Firstly, dicing is carried out on a wafer to separate it into semiconductor chips (S1). After a separated semiconductor chip is mounted on a body to be plated, die-bonding is carried out (S2). Then, the electrode pads of the semiconductor chip are connected to lead terminals formed in the body to be plated by wire-bonding (S3). The semiconductor chip is sealed with resin (S4), and exterior plating is applied to lead portions exposed from the sealing resin in a plating process (S5). A serial number and the like are marked on the sealing resin (S6). After removing the frame of the body to be plated, which connects the lead terminals with each other, lead formation/cutting and the like are carried out (S7). After a finishing process, sorting is carried out according to the external appearance (S8) and the characteristics and the likes (S9), and the manufacturing of the semiconductor device is completed with an inspection process (S10)
In this process flow, the thickness of plating formed around lead terminals is measured in the inspection process (S10). A method using a fluorescent X-ray film thickness meter has becomes widespread as a method of measuring a plating thickness. However, measurement of a plating thickness using a fluorescent X-ray film thickness meter requires a long measurement time. Therefore, inspections for plating thicknesses have been carried out by controlling the currents and the liquid composition as well as temperature to fixed values as described above and by verifying actual plating thicknesses by sampling inspections that are carried out for each batch of plating or at regular intervals.
Furthermore, although it is not exterior plating for lead frames, Japanese Unexamined Patent Application Publication No. 56-083936 (Patent document 1) discloses a method of measuring a plated film thickness in a manufacturing process in which a Schottky barrier diode is formed by forming plating on a semiconductor substrate. As shown in FIG. 11, a protection film 91 composed of insulating material has been formed on a semiconductor substrate 90. The protection film 91 has a monitoring opening 92 formed therein, and a plated film 93 is formed inside the monitoring opening 92. It should be noted that the thickness of the plated film 93 is larger in an area close to the protection film 91 (bulging portion) and is smaller in the central area distant from the protection film 91 (hollow portion). Note also that when the plated film 93 is viewed from the top, it is observed that the bulging portion has a circular shape (diameter d) that is concentric with the monitoring opening (diameter D). The diameter d of this concentric circle is measured, and the ratio of the diameter d of this concentric circle to the diameter D of the monitoring opening, i.e., ratio d/D is calculated. Then, as shown in FIG. 12, the film thickness of the plated film 93 is measured based on the d/D, i.e., the ratio of the diameter d of the concentric circle to the diameter D of the monitoring opening.